Ionizing radiation is a form of energy emitted by chemical elements or compounds that have an unstable electrical charge, which can be either positive or negative. The electrically-charged particles emitted are known as either alpha particles, beta particles, or gamma rays, and each type of radiation has various characteristic effects. Some heavy elements in nature naturally produce these effects, such as uranium, thorium, and radium, and the presence or close proximity of these materials in relation to the human body can be detrimental to human health. This is because ionizing radiation exists along a spectrum for radiation in general where it is responsible for much higher levels of energy emission than non-ionizing radiation, such as that produced by radio-wave broadcasts.

Forms of non-ionizing radiation that are considered relatively safe with controlled exposure include visible light waves, microwave energy, and infrared light, such as a toaster uses to heat bread. These forms of radiation have extremely long wavelengths compared to ionizing radiation and either lose power quickly with distance or can be easily reflected off of a surface. The danger of ionizing radiation exposure is largely due to the high frequency waves it is carried by, which can penetrate most materials to some degree and alter their chemical structure by breaking down normal chemical bonds.

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The types of ionizing radiation that commonly occur have varying levels of energy release. A typical ionization process for one atom or molecule releases 33 electron volts of energy to the surrounding area, which is sufficient to break most types of chemical bonds. This energy release level is considered especially important because it is capable of breaking the bonds between carbon atoms upon which all life forms on Earth are based.

Alpha particle emission, where two protons and two neutrons are involved, is produced by such radioactive elements like radon, plutonium, and uranium. They are the largest mass ionizing radiation particles, and this means that they cannot travel far before being stopped by a barrier. They lack the energy to penetrate the outer layers of human skin, but, if ingested through air or water, they have the potential to cause cancer.

Beta particle radiation is produced from free particles in an atomic nucleus that resemble electrons. These particles have much less mass than alpha particles, and can therefore travel farther. They also are produced by rare elements such as isotopes of strontium, cesium, and iodine. The effects of ionizing radiation from beta particles can be severe in large doses, leading to death, and they are one of the chief components of radioactive fallout from nuclear weapons detonations. In small amounts, they are useful for cancer treatment and medical imaging. These particles are also helpful in archeological research, as unstable elements of carbon such as carbon-14 can be used to date fossil remains.

Gamma ray ionizing radiation is produced by gamma photons that are often emitted from unstable atomic nuclei along with beta particles. Though they are a type of photon that carries light energy like normal visible light, a gamma photon has 10,000 times more energy than a standard white light photon. These emissions have no mass like alpha particles, and they can travel vast distances before losing their energetic charge. While often classified with x-rays, gamma rays are emitted by the atomic nucleus, whereas x-rays are emitted by electron shells around an atom.

Ionizing radiation regulations strictly limit exposure levels to gamma rays, though they are naturally occurring at low levels and are produced by the isotope of potassium-40 that is found in soil, water, and foods high in the element potassium. Industrial uses for gamma radiation include the practice of radiography to chart cracks and voids in welded parts and metal composites such as in high-speed jet engine turbines for aircraft. Radiation from gamma rays is considered by far to be the most dangerous form of radiation to living things in large doses, and it has been postulated that, if a gamma ray star 8,000 light years from Earth were to explode, it could destroy half of the Earth's ozone layer, making exposure to ionizing radiation from our own Sun much more detrimental to human health.

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